CREATE TRIGGER ACT_PARTICIPATION_TRG 
BEFORE INSERT ON ACT_PARTICIPATIONS 
FOR EACH ROW 
BEGIN
  <<COLUMN_SEQUENCES>>
  BEGIN
    IF :NEW.ACT_PARTICIPATION_ID IS NULL THEN
      SELECT ACT_PARTICIPATION_SEQ.NEXTVAL INTO :NEW.ACT_PARTICIPATION_ID FROM DUAL;
    END IF;
  END COLUMN_SEQUENCES;
END;
/
